The present invention relates to a line burner, and particularly, to a nozzle mixing line burner. Most particularly, the invention relates to a low emission, air/fuel mixing nozzle line burner that produces a short flame.
Line burners are known. Manufacturers and users of line burners generally desire a burner that is efficient and thus conserves energy. Efficiency is often measured by the burner's turn-down ratio. The turn-down ratio of a burner refers to a ratio of a maximum "firing rate" to a minimum firing rate for a particular burner assembly. The firing rate is the measure of how much fuel gas is consumed per hour (btu/hr). In industrial applications, a high turn down ratio is preferred because it reflects the burners ability to consume less fuel at the minimum firing rate (similar to a "low-idle" in an automobile). A typical premix-type line burner has a maximum turn-down ratio of 10:1 where ten times as much fuel is fed into the flame at the maximum firing rate than at the minimum firing rate.
Another desirable feature of a line burner is a minimal amount of hardware necessary to construct the burner. The reduction in hardware allows the manufacturer to manufacture the burners at a lower cost, the savings of which may be passed on to consumers.
One example of a known line burner is U.S. Pat. No. 5,057,008 to Dielissen which describes a raw gas burner nozzle with mixing plates through which combustion air flows to create the turbulence required for combustion. Another type of burner that pre-mixes the fuel and the air is shown in U.S. Pat. No. 5,236,350 to Cummings, III et al. For an additional example of a known burner, see U.S. Pat. No. 5,131,836 to Coppin. What is needed is a nozzle mixing line burner that creates locally lean combustion through most of its operating range and has a turn-down ratio well above that standard in the industry, without additional hardware.
One object of the present invention is to provide a nozzle mixing line burner having a nozzle body with fuel/air mixing channels angled relative to one another in a manner to cause impingement of air/fuel mixtures streaming into a combustion chamber to create a flame quality and emissions substantially equivalent to expensive ultra-lean combustors.
Another object of the present invention is to provide a nozzle assembly for use in a line burner that allows the line burner to have a turn-down ratio of more than 10:1 and preferably at least 20:1.
A burner apparatus in accordance with the present invention includes a line-burner combustion chamber and nozzle body coupled to the combustion chamber. The nozzle body is also formed for attachment with an air housing. The nozzle body includes two channels extending therethrough that are formed to pre-mix the air and fuel. Each of the channels include an inlet or opening for receiving air from an air supply plenum within the air housing and an outlet or exit for discharging a fuel/air mixture created within the channels into the line-burner combustion chamber.
In order to feed fuel into the channels, the nozzle body is formed to include a fuel-distribution chamber positioned between the channels. The fuel-distribution chamber is fed by a fuel supply line extending through the plenum of the air housing. In addition, at least one fuel passageway is formed between the fuel-distribution chamber and each of the channels so that fuel within the fuel-distribution chamber flows into the channels.
In preferred embodiments of the present invention, the nozzle body is formed to include a raw gas hole or delivery passageway extending between the fuel-distribution chamber and the line-burner combustion chamber. The raw gas hole is preferably positioned equidistant between the respective outlet and exit of the channels. Thus, the raw gas hole permits additional fuel to be fed to the line-burner combustion chamber to increase flame stability.
The nozzle body may be formed to include a plurality of channels positioned in a linear spaced-apart relation to one another along the line-burner combustion chamber to form one row of channel outlets and an opposite row of channel exits in said chamber. In addition, cooling air holes or delivery passageways extend between the air plenum and the combustion chamber. The cooling air holes are positioned in spaced-apart relation to one another between the outlets in one row and the exits in the second row. The cooling air holes allow the burner manufacturer to construct the combustion chamber from a lower grade of material.
In another embodiment of the present invention, the burner apparatus includes a line-burner combustion chamber and nozzle body coupled to the combustion chamber. The nozzle body includes two opposed slots that are formed to pre-mix the air and fuel therein and which extend along the length of the line-burner combustion chamber. The slots are formed similarly to the above-described channels, except that each slot itself forms a row extending across the line-burner combustion chamber. Illustratively, the two opposed slots are arranged to lie in spaced-apart parallel relation.
The burner assembly of the present invention creates a lean fuel/air mixture within the nozzle assembly and impinges jets of the mixture into each other to create flame stability, enhanced mixing, CO burnout, and NO.sub.x reburn. The burner assembly has the advantage of utilizing a common fuel-distribution chamber for both the fuel passages and raw gas channels without additional or separate piping or connections.
Advantageously, the turn-down ratio of the new burner is higher than any known premix line burner. The nozzle mixing line burner of the present invention can be operated at a turn-down ratio of at least 10:1 and as high as 40:1. Expensive premix equipment and flame arresters are not required by the new burner assembly of the present invention. In fact, flame propagation purposefully occurs back to the point of fuel injection in the burner of the present invention.
Additional objects, features, and advantages will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.